RFID is an automatic identification technology, relying on remote retrieval of data from relatively simple and inexpensive electronic devices called RFID transponders. RFID is a very promising technology and is expected to significantly benefit many fields, including commerce, medicine and security, to name just a few. However, despite its promise, RFID technology has thus far not been able to provide adequate robustness and reliability, which are essential requirements for many potential applications of the technology, without becoming too cumbersome and expensive.
The most common type of RFID transponders are passive tags. Passive RFID transponders have no internal power supply. In order to communicate with the RFID transponders, a central unit known as “the reader” emits radio frequency waves. The RFID transponder relies upon the signal from the reader for energy. For the RFID transponder to operate, an incoming radio frequency signal must induce a sufficient amount of current in the antenna of the tag to power the integrated circuit (IC) in the transponder and to enable the transponder to transmit a response.
It has been suggested to incorporate an internal power supply inside the RFID transponders to provide reliable energy. However, although an internal power supply can provide the energy needed to power-up the RFID transponder, active RFID transponders remain sensitive physical or electromagnetic barriers or obstacles in the path of a transmission from the RFID transponder to the reader (the uplink). For example, a RFID transponder attached to a package situated at the bottom of a relatively large stack of packages must overcome the physical obstacle created by the packages situated on top (and around) the package to which the transponder is attached, in addition to the greater physical distance to the reader. If the stack is large enough, the bottom transponders will not be able to reach the reader. On the other hand, the upper transponders have a much better chance of reaching the reader. The distance from the top packages to the reader is considerably shorter, and there are less packages (or non at all) in the path of the transmission to the reader.
What is needed is a method, a network and a circuit to enable an RFID transponder to relay a transmission from another RFID transponder. There is a further need for a method, a network and a circuit to enable two or more RFID transponders to relay a transmission from another RFID transponder in synchronous with one another. It is further needed to provide a method, a network and a circuit which enable RFID transponders to achieve substantially robust and relatively reliable communication.